In general, lithography is a necessary step in planar processing of microstructures and nanostructures. It is the step defining the in-plane shape of the structures. One may distinguish between lithographic systems employing a mask and systems not employing masks. The latter are referred to as maskless lithography systems. Lithographic systems employing a mask have the advantage of being able to replicate the mask pattern on substrates at high speed. This is the case in projection lithography, contact lithography, imprint lithography, EUV lithography, and x-ray lithography, which are typically used in high-volume production. The mask itself is typically fabricated using a maskless lithography system such as a scanning electron-beam lithography system, a zone-plate-array lithography (ZPAL) system, or a laser writer. Maskless lithography systems can generate virtually any pattern and do not replicate a pattern from a mask. However, this arbitrary pattern generation is typically much slower than mask replication. Hence maskless lithography systems ordinarily are not directly used in production. They are used primarily for prototyping and mask manufacturing.